Recently, provision of printed materials of various kinds and small lots is under progress, and attention is drawn to, as a substitute for off-set printing of a related art, an inkjet printing which is an on-demand printing made easy to respond to various kinds and small lots. Furthermore, compared to off-set printing of a related art, the inkjet printing is more convenient and has an advantage in terms of economic efficiency and energy saving.
The inkjet printing is a printing method in which fine ink droplets ejected from a printer head are landed on a recording medium, infiltrated and fixed to form dots, and in accordance with gathering of many of those dots, an image is formed. Ink for inkjet printing is required to have, in addition to physical properties related to image quality of a printed material or weather resistance, various properties including inkjet suitability such as ejection stability or intermittent ejection stability from a printer head.
Patent Literature 1 discloses an oil-based ink for a piezo-type inkjet printer containing a fixing resin, a pigment, and a specific solvent, as an ink that has no ink clogging in a printer nozzle during printing, an excellent ink ejection property and ejection recoverability, and an excellent fixing property to a material to be recorded and drying property. In Patent Literature 1, as the specific solvent, a combination of a specific cyclic ester and ethylene glycol monobutyl ether acetate is disclosed. Furthermore, as the fixing resin, a combination of an acrylic resin and a vinyl chloride-vinyl acetate copolymer resin is disclosed.
Patent Literature 2 discloses an oil-based ink composition containing a mixed solvent having specific polyoxyethylene glycol dialkyl ether and a lactone-based solvent at a specific ratio and a color material, as an oil-based ink composition for inkjet recording that is suitable for printing on a polyvinyl chloride substrate and is excellent in terms of any of print quality, printing stability, print drying property, and preservation stability of ink. Patent Literature 2 discloses that, as a binder resin for the oil-based ink composition, a combination of a (meth)acrylic resin and a vinyl chloride-vinyl acetate copolymer resin and/or a fibrous resin is used.
Patent Literature 3 discloses an ink composition for inkjet recording containing a mixture of specific diethylene glycol and specific dipropylene glycol as a solvent, as an oil-based ink composition for inkjet recording that can provide a high quality image with high gloss, excellent water resistance and friction resistance, and no feathering or bleeding. However, the aforementioned solvent used in the ink composition of Patent Literature 3 is easy to have clogging in a printer nozzle. Furthermore, because the solvent has poor solubility for the vinyl chloride-vinyl acetate copolymer, a content ratio of the copolymer cannot be increased. Thus, there are cases in which a printed material has insufficient optical density.
It is also required to have an additional improvement of resistance such as alcohol resistance and stretchability of a printed material to be obtained. When applied to a wall surface, for example, a printed material with excellent stretchability is not likely to generate cracks under stretching of wrinkles, and thus a change in color tone is suppressed.